A recorder quartet playing notes determined by the
topography and geography of the route followed by the 31
bus. The piece, like the bus journey lasts 22
minutes.
Musical notes are assigned from the numerical data, such as
map references and heights, by simple substitution, so, for
example, 3 becomes G and 7 becomes A In the case of the
street names, where a letter of the alphabet is not a note
from the musical scale, it is substituted systematically
for one that is. Thus CASTLE becomes CAEFEE and so
on.

The tenor recorder plays notes derived from the name
of the road the bus is on at the time. Each musical phrase
lasts the same length of time as the bus spends on that
road.

The treble plays a set of phrases dictated by the
distance travelled so far, the compass bearing, the time
elapsed and the change in direction since the last
checkpoint, which are at 100m intervals. The phrase plays
for the 24 seconds that the bus spends, on average, on each
100m section. Most of the time each phrase is played twice,
but on the steep uphill sections it plays once, while on
the steep downhill parts it plays three or even four times
in 24 seconds.

The descant line represents the spot heights above
sea level at 36 points along the route. The 8 note phrase
is derived from the grid reference, while the speeded up
repeat of the phrase is played once for each 10m above the
level at the start of the journey.

The sopranino "chimes" every minute with a "pip"
added for each minute elapsed.
The four parts were recorded separately and digitally
edited to conform, to within a few milliseconds, to the
appropriate parts of the bus route. Finally the tracks were
mixed together into one recording. There has been no
attempt to make the sounds into a pleasing musical
composition, the rules are strictly adhered to - at any
given moment the combination of notes heard is entirely
dictated by the rules set at the outset.